Zhang Xin-Zheng

Preparation and Size Characterization of Silver Nanoparticles Produced by Femtosecond Laser Ablation in Water

Femtosecond laser ablation of silver plate placed in water is used to produce nanoparticle suspension. The method is easy to operate and the suspension is relatively stable. The optical properties and the size distribution of the suspension are studied with UV–vis absorption spectroscopy and dynamic light scattering, respectively. The shape of the nanoparticles is investigated by an atomic force microscope, which is near spherical. There are two kinds of nanoparticles, small particles with diameter about 35 nm, and large particles with diameter about 120nm.

Laser-Driven Silver Nanowire Formation: Effect of Femtosecond Laser Pulse Polarization

We report our laser-driven method used to make large quantities of straight thin silver nanowires, and experimentally demonstrate that femtosecond laser pulse polarization has a prominent effect on formation of non-spherical shapes of nanoscale particles. Further, our experiment directly reveals that the underlying mechanism is plasmon-plasmon interaction, which can be controlled by polarization and plays a decisive role in this non-synthetic method for metal nanowire formation.

Raman scattering in In/InOx core—shell structured nanoparticles

The properties of Raman phonons are very important due to the fact that they can availably reflect some important physical information. An abnormal Raman peak is observed at about 558 cm−1 in In film composed of In/InOx core—shell structured nanoparticles, and the phonon mode stays very stable when the temperature changes. Our results indicate that this Raman scattering is attributed to the existence of incomplete indium oxide in the oxide shell.

Characterization of Photon Statistical Properties with Normalized Mandel Parameter

Normalized Mandel Parameter (Q) is introduced as a new measurement of photon statistics. Dependences of Mandel parameter Q and corresponding normalized Mandel parameter (Q) on photon-counting time interval are experimentally investigated for pseudo-thermal light. We demonstrate that (Q) is more appropriate than Q to measure the statistical deviation from Poisson distribution, because (Q) presents clearly both the intrinsic statistical properties and measuring effects. The advantages of (Q) in charactering nonclassical emissions are also discussed.

Saturable Nonlinearity in Photovoltaic-Photorefractive Crystals Under Open-circuit Condition

We show that the refractive index change induced by a focused incident beam with an additional incoherent uniform illumination in photovoltaic-photorefractive crystals under open-circuit condition has a saturable nonlinearity form. The incoherent uniform background illumination can be used to increase the effective dark irradiance. The formation time of the photovoltaic soliton can be decreased by keeping the intensity of the soliton at a higher value without over-saturation by use of the background illumination.

Time-Resolved Femtosecond Degenerate Four-Wave Mixing in LiNbO3:Fe,Mg Crystal

Forward degenerate four-wave mixing (DFWM) processes are investigated with a femtosecond pulsed laser in lithium niobate crystal doubly-doped with magnesium and iron (LiNbO3:Fe,Mg). The pulse energy dependence reveals a pure third-order nonlinear response, and the third-order nonlinear susceptibility χ(3) in the material is evaluated to be 4.96×10−13 esu. The time-resolved DFWM process shows a response time of χ(3) shorter than 100 fs, which is due to the nonresonant electronic nonlinearities. Our results indicate that LiNbO3 crystals have potentials for ultrafast real-time optical processing systems, which require a large and fast χ(3) optical nonlinearity.

Coherence preservation during light-surface plasmon polaritons-light transformation

We constructed a four-layer system composed of a prism, a silver film, an air layer and a lithium niobate crystal. Initially we used two coherent light beams to excite surface plasmons. The surface plasmons were then decoupled into light in the photorefractive crystal where a holographic grating was recorded. The two beams remained coherent through light to surface plasmons to light transformation. Studying the characteristics of the holographic grating we found out that the thickness of the grating was to the order of hundreds of microns. The thick holographic grating suggests that the holographic recording in the photorefractive materials was induced by the leaky waves rather than by surface plasmon polaritons directly.

Quantitative analysis of the self-absorption and reemission effects on the emission spectrum of photoluminescence in right-angle excitation—detection configuration

A theoretical approach based on differential radiative transport is proposed to quantitatively analyze the self-absorption and reemission effects on the emission spectrum for right angle excitation—detection photoluminescence measurements, and the wavelength dependence of the reemission effect is taken into account. Simulations and experiments are performed using rhodamine 6G solutions in ethanol as model samples. It is shown that the self-absorption effect is the dominant effect on the detected spectrum by inducing pseudo red-shift and reducing total intensity; whereas the reemission effect partly compensates for signal decrease and also results in an apparent signal gain at the wavelengths without absorption. Both effects decrease with the decrease in the sample concentration and the propagation distance of the emission light inside the sample. We therefore suggest that diluted solutions are required for accurate photoluminescence spectrum measurements and photoluminescence-based measurements.

Optically Controlled Coherent Backscattering from a Water Suspension of Positive Uniaxial Microcrystals

Coherent backscattering of light from a water suspension of zirconium silicate microcrystals is experimentally studied. Optically controlled weak localization of photons is realized, which is due to the reorientation behaviors of positive uniaxial microcrystals induced by a linearly polarized pump beam. Because zirconium silicate particles are positive uniaxial microcrystals, their reorientation behaviors are contrary to negative ones. Our work widely extends the materials used in the light-controllable weak localization of photons.

Photopolymerization-Induced Two-Beam Coupling and Light-Induced Scattering in Polymethyl Methacrylate

Light amplification due to two-beam coupling is realized in doped polymethyl methacrylate (PMMA) glasses. A coupling gain as large as 14 cm-1 is obtained. The dynamic behaviour of absorption and light-induced scattering due to the process of photopolymerization are also studied. The results show that the amplification and its dynamic process enable possible applications of PMMA in optical devices.